Calcium transport will be studied in terms of vitamin D-dependent calcium binding proteins found in intestinal mucosa and renal cortex. Studies are proposed to label these proteins and to study their metabolism after changes in calcium intake in normal or following the administration of vitamin D metabolites to vitamin D-deficient rats. In addition, calcium transport will be studied in Bacillus megaterium where energy-dependent calcium uptake by vesicles and the existence of a low molecular weight, non-protein calcium binder have been demonstrated. It is hoped to apply insights from these to problems of calcium absorption in patients.